Assuming you did the calculations correctly, a resistor dissipating 10W at 5v would be drawing 2 amps. Two in paralell would draw 4 amps and the resistor value of each would be 2.5 ohms.

This seems way more current than would be needed. I would guess - and it is a guess - that loading the power supply to 1 or 2% of its full rated power would be about the size of whats needed.

So One 10W resistor would be correct if it was a 1KW supply, supplying 1KW at 5volts and no other current. That would be a total maximum current of 200 Amps. But the 5v power supply in a 1KW PSU is often only 50W, (REad your PSU specs.) so in this case you would expect to plan for 0.5 watts of power drain if we assume 1%, and at 5 volts 0.5w is 0.1 amps, The required resistance would be 50 Ohms.

You only (potentially) need this if you are using 2 PSUs on one machine. The PSU thats only powering GPUs is only loaded on the 12v rail, which can be a problem. I assume you are using only 1 PSU, so you are powering the motherboard with it; in that case, there is no point in wiring light bulbs or resistors.

You only (potentially) need this if you are using 2 PSUs on one machine. The PSU thats only powering GPUs is only loaded on the 12v rail, which can be a problem. I assume you are using only 1 PSU, so you are powering the motherboard with it; in that case, there is no point in wiring light bulbs or resistors.

I get around this by powering a 5v enclosure fan(or two) with secondary PSUs

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You only (potentially) need this if you are using 2 PSUs on one machine. The PSU thats only powering GPUs is only loaded on the 12v rail, which can be a problem. I assume you are using only 1 PSU, so you are powering the motherboard with it; in that case, there is no point in wiring light bulbs or resistors.

I am using 2 PSUs on one mobo and I need to load up the 5V line to put some stress on the PSU that is only delivering through the 12V line etc.

I think I have the fan on 5v, I must give it a spin for it to start, might not happen on 7v,

It fixed my PSU problem (it's a 0.6 amp fan)

Thats a good idea. Instead of producing heat do something useful w/ the load. There are some fans which can start on 5V check reviews in silent PC forums/sites. I don't think running on 7V will help. The load is going to be on the 12V rail right?